This relates generally to testing wireless electronic devices, and more particularly, to calibrating test equipment that is used to test wireless electronic devices.
Wireless electronic devices typically include transceiver circuitry, antenna circuitry, and other radio-frequency circuitry that provides wireless communications capabilities. During testing, wireless electronic devices under test (DUTs) can exhibit different performance levels. For example, each wireless DUT in a group of DUTs can exhibit its own output power level, gain, frequency response, efficiency, linearity, dynamic range, etc.
The performance of a wireless DUT can be measured using an over-the-air (OTA) test station. An OTA test station includes a test chamber with an OTA antenna, a test unit, and a test host. The OTA antenna is connected to the test unit and is used in sending and receiving radio-frequency (RF) signals to and from the test unit. The test host is connected to the test unit and directs the test unit to perform desired functions during testing.
During test operations, a wireless DUT is placed into the test chamber and communicates wirelessly with the OTA antenna in the test chamber. Wireless transmissions of this type experience OTA path loss between the DUT antenna and the OTA antenna. Downlink and uplink OTA path loss can be respectively defined as the power attenuation of a radio-frequency signal as it propagates from the OTA antenna of the test chamber to the antenna circuitry of the wireless DUT and as the power attenuation of an RF signal as it propagates from the antenna circuitry of the wireless DUT to the OTA antenna of the test chamber.
An OTA test system typically includes multiple OTA test stations that are used to test multiple wireless DUTs in parallel. Each OTA test station typically includes its own test chamber, test unit, and test host. A production DUT is placed into the test chamber of each test station during product testing. Typical product testing involves measuring the wireless performance of each DUT and applying pass/fail criteria.
The radio-frequency path of each test station has its own unique OTA path loss characteristic. These unique path losses should be taken into account for accurate testing. In an effort to take into account these OTA path loss variations between test stations, a “golden” reference DUT is used to calibrate each test station. A golden reference DUT is a carefully selected DUT that exhibits desired wireless performance. Typically, a limited number of golden reference DUTs are produced, and each golden reference DUT has a limited testing lifetime. As a result, it can be difficult and costly to distribute the golden reference DUTs to different test sites for calibrating test stations.
It would therefore be desirable to be able to provide improved calibration techniques for calibrating OTA test systems.